I don't rightly know

I don't rightly know.

Rur. I do not know. Tom: When will Joe be getting back? Charlie: I don't rightly know. Jane: What's the difference between a first cousin and a first cousin once removed? Mary: I don't rightly know.
See also: know, rightly
References in classic literature ?
I think it's five-and-twenty, but I don't rightly know vether it ain't more.